The invention relates to an electric connection box for automotive wiring or the like, and more particularly to such an electric connection box which prevents leakage current from developing in a bus bar circuit when water intrudes into the electric connection box or when water droplets, due to condensation, deposit on the electric connection box.
An electric connection box of this general type shown in FIG. 4 comprises a circuit board 1 composed of an electrically insulative base plate 3 and a plurality of bus bars (circuit 2 mounted on the base plate 3 to form a laminated construction, a box body 4 accommodating the circuit board 1, and a lid 5 covering the base plate 3. Tabs 6 extending upwardly and downwardly from the bus bars 2 are inserted into a fuse case 7 and a relay cavity 8, mounted on the lid 5, and a connector mounting portion 9 mounted on the bottom wall of the box body 4, and are connected to their mating terminals of fuses, relays, wire harness terminal connectors, etc., if necessary, through female-to-female lugterminal strips (not shown).
When such an electric connection box is to be used, for example, in an engine room, a waterproof cover 10 is fitted on the electric connection box. However, there is a risk that at the time of washing, water under high pressure intrudes into the electrical connection box through locks 11a and 11b and other parts. Further, since the temperature at the time of the running of the engine greatly differs from the temperature at the time when the engine is stopped, condensation deposits on the inner surface of the cover. As a result, water droplets reach the bus bars 2 through terminal insertion holes 12 in the fuse case 7, etc., and the tabs 6 to wet the bus bars 2, thereby developing a leakage current between the bus bars 2. This causes a malfunction in the control system and corrosion of the bus bars.
To deal with the above problem, as shown in FIGS. 4 and 5, it has been proposed to cover the uppermost layer of the circuit board 1 with a waterproof plate 13 to entirely cover the bus bars 2 and the insulative base plate 3 (Japanese Utility Model Unexamined Publication No. 172216/88 published on Nov. 9, 1988 and owned by the same assignee). Seats 14 are formed on the upper surface of the waterproof plate 13, and each seat 14 has an insertion hole 15 for passing the tab 6 therethrough. The height h1 of the seat 14 is sufficiently greater than the diameter h2 of the water droplet G in an attempt to prevent the intrusion of the water droplet g into the insertion hole 15.
Although the waterproof plate 13 shown in FIGS. 4 and 5 effectively prevents the water droplets from reaching the uppermost layer of the bus bars 2, the plate cannot prevent fine water droplets, produced by condensation, from intruding into the interior through a gap between the tab 6 and the inner surface of the insertion hole 15. Once the water thus intrudes, the waterproof plate 13, which forms a kind of a sealed construction, prevents evaporation of the water. As a result, there is a risk that a leakage current will flow through the lower layer of bus bars 2A and 2B for a long period of time.